The present invention relates generally to structure for retaining an axle shaft within a housing and more particularly to structure for preventing axial movement of the shaft in a steerable axle where a double cardan constant velocity U-joint is used.
On steerable axles where a double cardan constant velocity U-joint is used, one end of the U-joint must be retained and the opposite end must have freedom for end play. This is because a characteristic of this type of joint is that as it moves through its operating angle, the length of the joint changes, resulting in reciprocating motion or "plunge" of one end of the joint as the axle is steered. It is not functional to allow the U-joint to float or in other words, fix both shaft ends with the U-joint not attached to either, since the U-joint can move off of the center of the steering axis. Therefore, it is necessary to fix or retain end play of either the inner or outer shaft along with one end of the U-joint.
In some applications, the shaft, inner or outer, which is allowed to plunge is important. For example, on a steerable mechanical front wheel drive axle with a limited slip differential, the plunge which can occur across the steering axis can be, depending upon the size of the unit, from 9 mm to 10 mm. If this plunge is allowed to occur on the inner part of the shaft, it can have a substantial effect on the limited slip action of the differential. Specifically, even though the inner shaft is free to slide within the limited slip unit, under load substantial friction between the unit and shaft would still cause excess friction between the disks during the shaft plunge. Therefore, it is extremely desirable that the inner shaft be held axially stationary with respect to the axial housing and that all plunge be taken on the outer side of the universal joint.
In holding the axle shaft against axial movement relative to the housing, it is also important that tolerances be held quite rigid since end play of 0.010" can be detrimental to an oil seal unless a special oil seal which can tolerate both axial and rotary movement is employed.
One design for preventing axial movement of the inner end of a drive shaft for a steerable mechanical front wheel drive axle is shown in U.S. Pat. No. 4,693,699 which issued on Aug. 15, 1987 and is assigned to the assignee of the present application. In the design shown in that patent, the axle housing and yoke are made of separate pieces and are together. The inner axle shaft is provided with an annular groove and two half washers are positioned in the groove and held between the axle housing and yoke. In this manner, axial movement of the inner shaft is tightly controlled and all plunge created by the universal joint is taken on the outer shaft where a special oil seal arrangement is employed. The design shown in U.S. Pat. No. 4,693,699 adequately controlled the axial movement of the inner shaft, but created manufacturing problems due to difficulties in heat treating the inner shaft across the groove for the retention ring.
In a design similar to that shown in U.S. Pat. No. 4,693,699, the assignee of the present application eliminated the need for a groove for the two half washers by reducing the diameter of the shaft back to a shoulder so that the two half washers bore against the shoulder and against a sleeve trapped between the two half washers and the inner end of the universal joint stub shaft. Both the design shown in the U.S. Pat. No. 4,693,699 and that previously utilized by the assignee of the present application relied upon the axle housing and yoke being made of separate parts bolted together in order to place the two half washers on the shaft. In some applications, it is desirable for cost saving reasons, if for no other reason, to have the axle housing and yoke made of a single casting.
Another prior art design known to applicant utilized a single piece axle housing and yoke and held the inner shaft from axial movement. In this design the inner race of a ball bearing was captured between a shoulder on the shaft and a snap ring in a groove of the shaft. The outer race of the bearing was captured between two snap rings positioned in internal grooves of a ring. The ring was then held in a fixed position with respect to the axle housing by a dogpoint screw which was threaded through the axle housing into a groove or hole in the outside surface of the sleeve. While this design did utilize a single piece axle housing and yoke, the use of multiple snap rings to retain the roller bearing, and the roller bearing itself, provided too much end play between the axle and axle housing such that it was difficult to maintain a seal between the axle and axle housing.